1. Field of the Invention
The present invention generally relates to oil well casing handling mechanisms referred to as spiders and elevators, which are used in the well drilling industry to effect the insertion and removal of drill stem and well casing segments into and from well bores of oil and gas wells, and more particularly to a combined well casing spider and elevator which may be used interchangeably as the spider or the elevator and having a laterally pivotal gate member which permits ease in the entry and removal of a drill stem and/or well casing segment. Even more specifically, the present invention incorporates means for achieving enhanced slip opening characteristics while preventing inward tilting of the slips and means providing for controlled spider operation while minimizing wear of spider actuating components and also means for ensuring smooth release of the slip open latch with which the spider and elevator mechanism is provided.
2. Background of the Invention
In the specification and the appended claims, reference will only be made to the gripping, release, insertion and removal of a well casing, but it is to be expressly understood that the combined well casing spider and elevator according to the invention is not limited in its use to well casings alone and can be used with well casings, drill stems and other pipe or rod-like members.
To effect the lowering and raising of long strings of well pipe such as oil well casings, a spider is conventionally mounted over the rotary table on the working platform of an oil well drilling derrick. The spider is operable to grip or release a segment of the well casing by the action of slips which provide a gripping and holding action as a downward force is applied to the slips by the weight of the casing and release the gripping and holding action as the casing is moved upwardly relative to the spider. An elevator attached to a hoist co-operates with the spider in the lowering and raising of well casing and is also operable to grip or release the well casing. Well casing is removed, for example, by lowering of the elevator so that it can grip the end of the well casing extending above the spider. The spider then releases the well casing and the elevator is hoisted until the end of the next segment of well casing extends above the spider. The spider again grips the well casing, and the casing segment removed by the elevator is disconnected by rotating and unthreading it. This segment can then be off loaded from the drilling rig to a pipe rack located adjacent the rig, thus allowing the elevator to be again lowered to grip the end of the well casing projecting above the spider to repeat the process.
Conventionally, a casing spider is provided with a plurality of arcuate wedge-shaped scepter-like elements of slips formed of cast metal such as steel which are borne by a spider bowl which is hollow and whose interior surface tapers upwardly and outwardly. These slips ride on the internal tapered surface of the spider bowl, being normally keyed thereto, and means is provided for raising and lowering of the slips in contact with the tapered surface of the hollow spider bowl such that, when the slips are raised, they are caused to move radially away from each other to increase the size of the opening defined by the slips through which passes the well casing. Conversely, when the slips are lowered with respect to the spider bowl defined by the spider housing the slips are caused to move radially toward one another so that the inner gripping surfaces of each of the slip segments moves into gripping relation with the casing. One such type of well spider is shown in U.S. Pat. No. 2,274,273, issued Feb. 24, 1942, to Earl J. Miller.
Though the combined spider and elevator set forth in the '488 Patent of Gray effectively overcomes deficiencies of the well spider mechanism of the '273 Patent of Miller by combining the features of a well casing spider and an elevator in a single unit having a lever operated lift mechanism for moving driven and floating slip segments to the radially expanded or release positions thereof, it has been determined that certain shortcomings of the spider-elevator mechanism of Gray exist which warrant improvement. The '488 Patent of Gray teaches the use of rollers carried by lift arms which react against external upwardly and outwardly tapered surfaces of the main body and which move the lift arms and thus the slips outwardly to the casing releasing positions thereof. Though the slip segments are moved to their retracted or open positions, thus releasing the casing, radial slip movement is slight so that it may be difficult to run a section of casing into the slip opening. Additionally, due to the loose tolerance of fit of the slips with the slip guide slots of the body or bowl structure, the slips, or some of them, can tilt inwardly with the upper ends thereof essentially closing the slip opening or at least interfering with movement of the casing into the slip opening. When this undesirable condition exists the downwardly moving casing can strike the slip segment in a manner causing damage to the slip segments, the casing or both. Accordingly, it is desirable to provide a spider-elevator mechanism having the capability of forcing the upper ends of the slips radially outwardly to an extent overcoming inadvertent slip closing movement and positively positioning the slip segments at a "more open" retracted position than is typically accomplished and preventing any inward tipping of any of the slip segments so that the slips will not interfere with movement of casing into the slip opening.
According to present practice the spider-elevator assembly of Gray has been manufactured using guide rollers which ride on outwardly facing guide surfaces of the housing or bowl and being shown at 106 in FIG. 5 of the '488 patent of Gray. These guide rollers readily become fouled, worn and require frequent replacement due to the presence of abrasive particulate such as drilling fluid, sand, dirt, dust and grease on the working floor of a drilling rig. In practice, because of the presence of abrasive particulate from drilling fluid, grease and other contaminants about casing spiders which cause rapid deterioration of roller bearings or bushings, the combination spider and elevator mechanism of Gray has been manufactured with actuating bosses on the lifting arms which replace the actuating rollers shown at 106 in the '488 Patent. These actuating bosses are in sliding contact with external upwardly and outwardly inclined guide or cam surfaces of the main spider body to provide the same slip spreading function as the rollers 106. It has been found however that the actuating bosses, being composed of metal and having sliding contact with externally facing body surfaces and operating in the presence of abrasive particulate, while more serviceable as compared with rollers, nevertheless are subject to accelerated wear of both the actuating bosses and the external guide or cam surfaces of the body structure. It is desirable therefore to provide slip expanding means which is not subject to exceptional wear, even in the presence of abrasive particulate, grease and other contaminants often found on well drilling rigs and which provides an efficient slip spreading function to ensure optimum positioning of the slip members, especially in the upward and radially retracted positions thereof.
As the slips of the combined well casing spider and elevator tend to reach the upward extent of the releasing movement thereof, the slips typically have minimal supported contact with the tapered inner surface of the main body and thus are susceptible to the upper portions of the slips tilting radially inwardly to positions potentially interfering with casing that is being lowered into the central opening of the well casing spider. To simply increase the height of the interrelating tapered surfaces of the main body or bowl and the slips would require significant increase in the overall height of the spider and would therefore be undesirable because vertical space requirement are critical on most drilling rigs. It is desirable therefore to provide a combined well casing spider and elevator which has the capability for causing significant radial expansion of the slips and which overcomes the problem of the upper ends of the slips tilting inward when the slips are opened, without requiring an increase in the overall height of the spider body or the slips.
The combined well casing spider and elevator of the '488 Patent of Gray incorporates a locking mechanism for locking the slip mechanism in the upward, release position thereof. As the slip operating lever 62 is pivoted downwardly about the cross-rod 60, moving the crank arm pivotally to the open position shown in FIG. 4B, the spring loaded indent pin 114 will rotate to its locking position with respect to a hardened steel plate 144 located at the bottom edge of the crank arm. To release the crank arm from this locked position, the indent pin is rotated against the bias of its compression spring 140, causing the tapered camming surface 146 to react with the hardened steel plate 144 as shown in FIG. 12A and drive the pin 114 linearly to release the crank arm and allow it to pivot as the weight of the slips moves the crank arm back to the broken line position of FIG. 3. It has been determined that accelerated wear of the tapered indent pin, especially at the tapered surface 146 and the intersection with the tapered surface 146 with the cylindrical pin surface occurs as the pin is rotated to its release position by rotating the release arm 74 by pulling on the lanyard 72. It is desirable therefore to provide a tapered indent pin that resists wear as it is rotated from its latched position to its release position.
The cross-shaft of the slip raising and lowering mechanism extends across the body structure, with the shaft ends being supported by journal bushings. On one side of the body structure one of the crank arms is secured to the cross-shaft at a location adjacent one of the journal bushings. At the opposite side of the body structure the opposite crank arm is secured to the cross-shaft at a location adjacent the other journal bushing and the actuating lever 62 is then fixed to the cross-shaft at a location outboard of the body structure. During extended operation of the spider-elevator unit it was found that the crank arms would move linearly relative to the cross-shaft and thus one or both of the crank arms could get out of adjustment with the cross-shaft, thus causing uneven raising and lowering of the slips. It is thus desirable to provide a cross-shaft assembly which is designed for positive location of the crank arms with respect to the cross-shaft and which prevents linear movement of the crank arms on the cross-shaft. This feature effectively prevents the slip raising and lowering mechanism from getting out of adjustment during normal operating conditions of the spider-elevator mechanism.